Upon occurrence of a disaster, such as an earthquake, for example, for reasons of confirmation of the safety of acquaintances, a large number of call-connection requests are made to communication networks, such as a mobile telephone network, from mobile phones and fixed phones. However, since the number of calls which can be processed by apparatuses, such as exchanges and servers, installed on the communication networks are limited, it is difficult to process all of the call connection requests. Further, in the worst case, the whole of the communication networks may not function well. In order to prevent occurrence of such a condition, in the case where excessive overloading on the networks arises, restriction control is performed on a fixed proportion of call connection requests from user terminals, for example, by an announcement of a guidance message such as “Calls are unlikely to be connected. Call again after a while.”
FIG. 1 is a schematic diagram illustrating an example of a method for controlling restriction on call connections, in which call congestion has arisen. FIG. 1 indicates a case where, for example, a mobile telephone network 900 is requested to connect calls under the condition where, due to occurrence of a disaster or the like, congestion of call connection requests from mobile phones has arisen. Existing restriction control of mobile phones is performed basically in accordance with subscriber classes set for individual mobile telephone users. A few VIP user terminals belong to a class which allows them to be call-connected with high priority, and therefore, are relatively likely to be call-connected even under the condition where congestion occurs; however, most of normal user terminals, which belong to a class of the lowest priority, are unlikely to be able to make phone calls under the condition where restriction control due to arising of congestion is performed. Further, since most of normal user terminals belong to the same class, as a result, a uniform restriction 910 is executed for normal user terminals 1-1, 1-2, . . . , 1-n. For example, a 90%-restriction is uniformly imposed on normal user terminals 901-1, 90-2, . . . , 90-n. That is, all terminals become subject to a condition where they can make phone calls on average only at a rate of one out of ten call connection requests therefrom.
However, in the following cases, it is difficult to say that good services are provided when performing such a uniform restriction control on all user terminals.
(A1) When a disaster occurs, people are likely to be living in groups, such as a family. In this case, provided that making a phone call with any one of family members is enabled, it is possible to confirm the security of all of the family members. However, in an existing method, since the same restriction control is performed on all the family members, a degree of difficulty in call-connecting a mobile phone is the same for each of the family members, regardless of the number of the family members.(A2) Upon occurrence of a disaster, in some cases, public telephones, which are likely to be call-connected more frequently than regular telephones, may be temporarily installed at evacuation places; however, this method needs a lot of cost and time. In contrast, in the case of a mobile phone, a lot of people own mobile phones, and utilization of them suppresses increase of cost and time. However, under the present situation, since the same restriction control is performed on all the user terminals, all the terminals fall into a state in which they are unlikely to be call-connected, and as a result, the mobile phones remain unable to be effectively utilized.
In order to overcome the foregoing disadvantages (A1) and (A2), Japanese Laid-open Patent Publication No. 2002-16976 discloses a method, which allows user groups to be created at a server side, and allows each of the groups to be supplied with a certain clock time during which call connections from the group are preferentially allowed. However, in this method, there are some limitations described below.
(B1) Clock times at which call connections are allowed are restricted.
(B2) Setting of the groups is performed at the initiative of a network side, and therefore, users cannot intervene in the setting. Accordingly, for example, the disadvantage (A1) cannot be solved. That is, it is not possible to perform such a control that any one of family members is allowed to make a phone call to confirm the safety of all the family members.
Although a mobile telephone network is depicted as a representative example in FIG. 1, the same is in the case of a fixed telephone network, the similar situation can occurs. Upon occurrence of a disaster, for example, call connections associated with individual fixed phones of houses located in the same region are uniformly restricted, and this restriction may cause occurrence of the similar situation in which the fixed phones of all houses located in the region are unable to make phone calls.